Field of the Invention
The invention lies in the semiconductor processing technology field. More specifically, the present invention relates to a method for applying a protective coating to a bottom surface of a semiconductor wafer or to the bottom surface and all four lateral surfaces, including edges and corners, of partially singulated or presawn semiconductor dies which are still in wafer form, especially with regard to the mechanical protection of backside, corners, and edges of semiconductor chips during final singulation of integrated circuits on the wafer, the wafer is diced by sawing or etching along parallel lines. During the sawing process, the edges of the chips are subject to various damage sources, such as splitting or chipping. In addition, with the increasing volume of flip-chip-in-package and waferlevel package, the handling of bare dies without convention packages in component test and assembly of the fragile silicon corners and edges of the dies. According, a protection of the semiconductor dies is required.
U.S. Pat. No. 6,023,094 to Kao et al. describes a semiconductor wafer having a bottom surface protective coating. That protective film on the bottom surface is intended to aid in preventing chipping during the wafer dicing process, and is formed by any process suitable for applying a thick film. In one embodiment, a screen printing process is utilized. There, a screen is placed over the bottom surface and the material to be deposited is dragged by means of a squeegee. By way of another example, a spinning type process may be used, wherein a thick film is spread across the bottom surface of the wafer.
A holding structure is utilized to protect the wafer during the application of the thick film. The wafer is mounted onto a mounting tape, the thick protective film facing the mounting tape. Any suitable cutting device is utilized to separate the dies from one another. Additionally, the protective film is intended to improve adhesion to the mounting tape, making it possible to use mounting tapes with inferior adhesion strength.
It is accordingly an object of the invention to provide an improved method for applying a protective coating to a bottom surface of a semiconductor wafer, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which provides sufficient protection against damage and allows for easy processing.
In addition, it is an object of this invention to provide a mechanical protection of backside, corners, and edges of semiconductor chips during final singulation and subsequent handling and assembly.
With the foregoing and other objects in view there is provided, in accordance with the in invention, a method of applying a protective coating to a bottom surface of a wafer, or to the bottom surface and all four lateral surfaces, including edges and corners, of partially singulated or presawn semiconductor dies which are still in water form which comprises the steps of:
forming trenches in a top surface of the wafer;
applying a top side dicing tape to the top surface;
grinding the wafer at a bottom surface opposite the top surface and thereby laying open the trenches;
applying a protective material on the bottom surface and filling the trenches; and
hardening the protective material to form a protection layer.
The forgoing method is advantageously applied to the final dicing of a semiconductor wafer with the protective coating in place. In that case, the following additional steps are performed:
fixing the protection layer to a mounting tape for fastening the wafer onto a dicing frame;
removing the top side dicing tape;
dicing the wafer into dies through the hardened protective material previously formed in the first dicing trenches; and
picking the dies off the mounting tape.
With the above and other objects in view there is also provided, in accordance with another embodiment of the invention, a method of applying a protective coating to a bottom surface of a wafer or to the bottom surface and all four lateral surfaces, including edges and corners, of partially singulated or presawn semiconductor dies which are still in wafer form, which comprises the steps of:
forming trenches in a top surface of the wafer;
applying a top side dicing tape to the top surface;
grinding the wafer at a bottom surface opposite the top surface and thereby laying open the trenches;
applying a glue layer onto a mounting tape; and
mounting the wafer on the mounting tape and causing the glue to fill the trenches.
Again, this method is expediently utilized in a method of dicing a semiconductor wafer, which comprises:
applying a protective coating to a bottom surface of the wafer as above, and further
removing the top side dicing tape;
dicing the wafer into dies through the hardened protective material previously formed in the first dicing trenches; and
picking the dies off the mounting tape.
Finally, there is also provided, in accordance with the invention, a method of applying a protective coating to a bottom surface of a wafer, which comprises the following steps:
applying a protective foil onto a mounting tape; and
mounting a bottom surface of the wafer onto the mounting tape with the protective foil facing the wafer.
The method is advantageously utilized for dicing a semiconductor wafer, whereby the following steps are performed:
applying a protective coating to a bottom surface of the wafer or to the bottom surface and all fours lateral surfaces, including edges and corners, of partially singulated or presawn semiconductor dies which are still in wafer_form as outlined above; and further
dicing the wafer including the protective foil into dies; and picking the dies with the protective foil off the mounting tape.
In accordance with a concomitant feature of the invention, the mounting tape is a UV-foil; and the step of picking off the dies includes applying UV-radiation to separate the UV-foil from the protective foil.
Once more in summary, to achieve the foregoing and other objects, the present invention provides a new backside treatment of the wafer. Trenches are cut into the top surface of the wafer by sawing or etching, and after grinding the wafer from the bottom side, a protective material is applied as a surface layer to the bottom surface while filling the trenches with this material. The material is hardened in order to accomplish the subsequent sawing process. In another embodiment of the present method, a double foil layer is applied to the rear side of the wafer including a mounting tape and a protective layer facing the wafer rear side.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for applying a protective coating to a bottom wafer surface or to the bottom surface and all four lateral surfaces, including edges and corners, of partially singulated or presawn semiconductor dies which are still in wafer form, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.